zoology and botany, microscopy, etc. 523 



alloys of any one metal grouped together. Though the work has all 

 been published elsewhere * the collection in a more compact form of the 

 accurate data obtained should prove useful. 



Constituents of Steel.f — H. le Chatelier attempts a much needed 

 definition of the constituents of the iron-carbon alloys. They are 

 classified as elements (ferrite or pure iron, and graphite or pure carbon), 

 compounds (cementite Fe 3 C is the only example), solid solutions, 

 aggregates, and possibly emulsions or colloidal solutions. The allotropic 

 varieties of iron may also be classed as constituents. Two solid solutions 

 are known, austenite (carbon, or carbide of iron, in y-iron), and mar- 

 tensite (the same in a-iron). As constituent x, the nature of which is 

 doubtful, the author deals with troostite, osmondite, troosto-sorbite, and 

 the sorbite of Stead. Its general characteristic is that of assuming a 

 deep black coloration upon etching with dilute acids. Constituent x 

 may be a solid solution or an aggregate of very finely divided elements. 

 The work of Charpy and Grenet would indicate that it is a very 

 intimate mixture of ferrite and cementite. Pearlite and the sorbite of 

 Osmond (incompletely formed pearlite) are aggregates, composed of 

 ferrite and cementite. The part played by /?-iron, and the constitution 

 of x, are still open questions. 



F. Osmond J points out that the hard austenite obtained by some 

 workers is in reality martensite. As to the constitution of martensite, 

 its magnetic behaviour indicates that the whole of the iron is not in the 

 a state, probably the remainder is /3, while the carbon exists as a pseudo- 

 solution. Stead appears to use the term sorbite in the same sense as 

 Osmond. Constituent x may be identified with troostite. 



Metallography at the National Physical Laboratory. § — The 

 annual report contains a section describing the year's work in the 

 metallurgical department. As a preliminary to the investigation of 

 the ternary system alaminium-copper-manganese, the binary system 

 aluminium-manganese has been studied. The alloys containing 30- 

 65 p.c. manganese disintegrate spontaneously from the solid cast state 

 into a fine crystalline powder. The results of the inquiry into the 

 various methods of obtaining cooling curves have been published else- 

 where. Crystalline silica has a well marked recalescence at 580° C. For 

 the research on eutectic alloys the lead-tin system was chosen. Equi- 

 librium was reached only by exposure of the alloys to a temperature of 

 175° C. for several weeks. The limit of solid solubility of tin in lead 

 appears to lie near 17 p.c. tin — a much higher percentage than has 

 hitherto been supposed. Oxide of chromium was found to give good 

 results in the polishing of very soft metals. Some progress has been 

 made in the photomicrography of metal sections by ultra-violet light ; 

 the Zeiss apparatus is described. Monochromatic blue light may be 

 used for approximate focusing and for the other preliminary adjust- 

 ments. The difficulties of the method are, however, serious, and sharp 

 photographs at high magnifications have not yet been obtained. 



* Zeitschr. Anorg. Chem., 1904, to present date. 



t Rev. de Metallurgie, v. (1908) pp. 167-72. J Tom. cit., pp. 205-6. 



§ National Physical Laboratory Report for 1907. 



